I just run the certification kit against my Metro app (using Json.net 4.5.5) and it failed with this error

Supported APIs

Error Found: The supported APIs test detected the following errors:

API System.Reflection.Emit.DynamicMethod in SYSTEM.REFLECTION.EMIT.LIGHTWEIGHT, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.Label in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.LocalBuilder in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.DynamicMethod.#ctor(System.String,System.Type,System.Type[],System.Reflection.Module,System.Boolean) in SYSTEM.REFLECTION.EMIT.LIGHTWEIGHT, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll
calls this API.

API System.Reflection.Emit.DynamicMethod.#ctor(System.String,System.Type,System.Type[],System.Type,System.Boolean) in SYSTEM.REFLECTION.EMIT.LIGHTWEIGHT, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls
this API.

API System.Reflection.Emit.DynamicMethod.GetILGenerator in SYSTEM.REFLECTION.EMIT.LIGHTWEIGHT, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.DefineLabel in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.Emit(System.Reflection.Emit.OpCode) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.Emit(System.Reflection.Emit.OpCode,System.Int32) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.Emit(System.Reflection.Emit.OpCode,System.Reflection.Emit.Label) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.Emit(System.Reflection.Emit.OpCode,System.Reflection.ConstructorInfo) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this
API.

API System.Reflection.Emit.ILGenerator.MarkLabel(System.Reflection.Emit.Label) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.DynamicMethod.set_InitLocals(System.Boolean) in SYSTEM.REFLECTION.EMIT.LIGHTWEIGHT, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.DeclareLocal(System.Type) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.Emit(System.Reflection.Emit.OpCode,System.Type) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.Emit(System.Reflection.Emit.OpCode,System.Reflection.FieldInfo) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.Emit.ILGenerator.Emit(System.Reflection.Emit.OpCode,System.Reflection.MethodInfo) in SYSTEM.REFLECTION.EMIT.ILGENERATION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

API System.Reflection.TypeInfo.get_Module in SYSTEM.REFLECTION, PUBLICKEYTOKEN=B03F5F7F11D50A3A is not supported for this application type. Newtonsoft.Json.dll calls this API.

Impact if not fixed: Using an API that is not part of the Windows SDK for Metro style apps violates the Windows Store certification requirements.

How to fix: Review the error messages to identify the API that is not part of the Windows SDK for Metro style apps. Please note, C++ apps that are built in a debug configuration will fail this test even if it only uses APIs from the Windows
SDK for Metro style apps. See the link below for more information: Alternatives to Windows APIs in Metro style apps.